TOKYO -- It's not yet five in the morning but the auction floor at Tokyo's fish market hums with activity as traders pace between rows of frozen tuna, examining them with flashlights and touching them with practised fingers.

With a shout of "Good morning!" an auctioneer launches into a rapid chant, knees bending rhythmically and fist pumping the air, as men in front of him signal subtly with their hands.

In moments it is over and a huge tuna, more than a metre (yard) long, is dragged away. By evening it will be on tables around the city, commanding top prices from eager diners.

"Tuna's the best, the king of fish," said Keiichiro Watanabe, a second-generation tuna wholesaler at Tsukiji market, as men behind him cut frozen tunas apart with saws and long knives.

"You can eat it and eat it and never get tired of it."

Tighter international fishing quotas, however, are now set to cut into the number of tuna that can be caught, biting into supplies of the fish dearest to Japanese hearts.

"I eat tuna at least once a week," said Naoto Hoshi, a 24-year-old medical student standing in an alley of small restaurants at Tsukiji after finished his sushi breakfast.

"If the price rises I'll be really unhappy. There just isn't anything else like tuna -- we Japanese can't live without it."

To feed its tuna hunger, Japan ranges far and wide. Tuna lined up on the auction floor one recent morning came from Libya, Greece, Bali, Australia and New York as well as Japanese ports.

So Japan was rocked last month by news that global quotas for Atlantic bluefin tuna -- a prized, high-end sushi ingredient -- will be cut by nearly 8 percent next year. Japan eats more than half the world's bluefin, which in October sold for an average 3,145 yen ($27) a kg at Tsukiji.

SLASHING QUOTAS

The previous month, Japan's quota for southern bluefin was halved for the next five years as punishment for years of overfishing. Worse may lie ahead.

Talks are being held in Samoa this week on conserving big-eyed and yellowfin tuna, which are often sold as sashimi in supermarkets, making them the tuna of choice for most consumers.

Some experts want catch reductions of 25 percent for big-eyed tuna and 10 percent for yellowfin, saying that if fishing continues at current levels, the stocks could be in trouble soon.

Japan opposes such restrictions.

"Our stance on quotas is that we need to obey them to preserve the resource," a Fisheries Agency official said. "But in this region there doesn't appear to be an immediate problem."

Fisheries experts disagree.

"Most tuna species are fully exploited, overexploited or depleted," said Jacek Majkowski with the Food and Agriculture Organisation in Rome. "What's alarming is that regardless of the status of the stocks, the global catch tends to increase."

Overfishing also means that the tuna being caught are smaller and younger, reducing the fat content for which sushi fans pay top money. The meat of famed tuna from Oma in northern Japan can go for up to 10,000 yen a kg, bringing the value of one fish haggled over on the auction floor as high as 2 million yen ($17,000).

Global health consciousness also means Japan faces rivalry for fish from nations such as the United States and China.

"The market, the tradition, started in Japan, but is really expanding," Majkowski said. "Japan is obviously a player, and a very significant player, but it is not the only player."

Despite tuna's present popularity, Japanese have really only eaten the fish for the past 200 years or so, with the fattier meat gaining favour in the decades since World War Two.

A recent media survey found that 19 percent of consumers wouldn't change their tuna eating habits if prices rose.

But 27 percent said they would switch to cheaper types of tuna, and 43 percent said they would cut down on tuna and eat less expensive fish instead. Eleven percent said they'd switch to meat.

"It depends on how expensive tuna gets, but I'll still keep eating it," said Takako Tomita as she ate a sushi breakfast before heading for her office. "That's how much I like it."

Still, even wholesaler Watanabe said the quotas made sense.

"The resources are limited so Japan has to take a bit less, since the rest of the world wants more," he said. "That's only natural.